Conventional approaches to steering a rocket-propelled vehicle employ an attitude control system (ACS) for directing the thrust of the rocket engine. Thrust vector control (TVC) approaches generate torque needed for attitude control and may be employed in both endoatmospheric and exoatmospheric vehicles in some cases. When steering a rocket-propelled vehicle, there is an intimate connection between the thrust of the main rocket motor and the needed torque to maintain attitude control. High performance rocket motors typically have thrust misalignment errors of between 0.15° and 0.25°. TVC systems can compensate for thrust misalignment by redirecting the thrust by an appropriate angle relative to the vehicle. The needed torque is approximately the thrust times the distance between the nozzle of the rocket motor and the center-of-mass of the vehicle times the misalignment error expressed in radians
Conventionally, TVC for rocket-propelled vehicles is performed using jet vanes, a gimbaled nozzle, a gimbaled engine, multiple engines with variable thrust, or a vectoring exhaust nozzle. Also, low thrust spacecraft may make use of other torque generation techniques, such as reaction wheels, control moment gyros, and magnetic torque coils.
Movable mass has also been considered for generating torque and controlling the attitude of a vehicle when external forces (e.g., thrust and aerodynamic forces) are applied to the vehicle. As used herein, movable mass denotes one or more volumes of mass that can be moved to sufficiently alter the location of the center-of-mass of a vehicle for flight control purposes. “Movable mass” and “movable masses” are used interchangeably. Movable masses have been analyzed and computer simulated for kinetic kill vehicles. However, such movable masses have always been internal to these vehicles, and furthermore, they have not been applied specifically to mitigating thrust misalignments. Also, TVC systems and movable mass systems have not been applied to small rocket-propelled vehicles, e.g., rocket motors with a mass of a few kilograms and nozzle dimensions of a few centimeters. Accordingly, an alternative ACS that may be configured for such vehicles may be beneficial.